I have a ps image that I want to convert to a gif image with horizontal by vertical dimensions of 900 and 800 respectively. I have tried to use the command:
convert panel.gs -resize x800 y900 panel.gif
or also:
convert panel.gs -resize 900x800 panel.gif
Can you help me to tweak the convert commands so I can get the desired results?
.gs is not a valid suffix. Did you mean .ps?
Imagemagick will need ghostscript as a delegate. You did not say what was wrong nor what platform or what version of Imagemagick.
If the image does not have the same aspect ratio as the final dimensions you want, you will either 1) need to distort it to fit using !, 2) resize it and then extend to the size you want filling with background color, or 3) resize it with ^ and crop it to the size you want.
convert panel.ps -resize "900x800!" panel.gif
convert panel.ps -resize 900x800 -gravity center -background white -extent 900x800 panel.gif
convert panel.ps -resize "900x800^" -gravity center -extent 900x800 panel.gif
Well, firstly you haven't actually said what's wrong with the two commands that you have tried already.....
Your PostScript program probably does not contain an 'image' as such, PostScript is not a bitmap format its a programming language.
You can use Ghostscript to render the PostScript to an image, and then use ImageMagick to resize that image, possibly you can combine these two steps, or just perform a single conversion, it depends on what exactly you want to happen, which isn't clear.
If (for example) your PostScript program requests a media size of 9 inches by 8 then you can create a bitmap image by simply setting the resolution to 100 dpi using -r100.
If you want the image scaled differently in each direction, then you need to set a non-square resolution. For example if the PostScript program requests media of 9 inches by 4 then you need to set the resolution to 100x200 in order to get an image exactly 900 x 800 pixels. You would use -r100x200 for this.
The alternative, from a PostScript point of view, is to set the media size to a given
value in pixels (using -g900x800) and set -dDFIXEDMEDIA which prevents the PostScript program from changing it. You can then use -dFitPage which will have Ghostscript scale the content to fit the page. However it will scale the content equally in both directions, which may leave white space around the edge.
Now since Ghostscritp doesn't write GIF directly you'll need to load whatever bitmap format you select into IM in order to write it out as a GIF, so perhaps the simplest solution is just to use Ghostscript to render the PostScript to a defined resolution (eg 100 dpi) and then load that image into IM and rescale it there.
Since IM (and therefore convert) use Ghostscript to process PostScript programs, that's what's happening now so it isn't obvious to me what your problem is.
How can I set a transparent background on JPEG image? This is a doubt of many colleagues of mine.
What would be the solution using Paint on Windows?
What are the other simple alternatives?
You can't make a JPEG image transparent. You should use a format that allows transparency, like GIF or PNG.
Paint will open these files, but AFAIK it'll erase transparency if you edit the file. Use some other application like Paint.NET (it's free).
Edit: since other people have mentioned it: you can convert JPEG images into PNG, in any editor that's capable of working with both types.
If you’re concerned about the file size of a PNG, you can use an SVG mask to create a transparent JPEG. Here is an example I put together.
JPEG can't support transparency because it uses RGB color space. If you want transparency use a format that supports alpha values. Example PNG is an image format that uses RGBA color space where (r = red, g = green, b = blue, a = alpha value). Alpha value is used as an opacity measure, 0% is fully transparent and 100% is completely opaque. pixel.
JPG does not support a transparent background, you can easily convert it to a PNG which does support a transparent background by opening it in near any photo editor and save it as a.PNG
How can I set a transparent background on JPEG image?
If you intend to keep the image as a JPEG then you can't. As others have suggested, convert it to PNG and add an alpha channel.
JPG doesn't support transparency
Just wanted to add that GIF "transparency" is more like missing pixels. If you use GIF then you will see jagged edges where the background and the rest of the image meet. Using PNG, you can smoothly "composite" images together, which is what you really want. Plus PNG supports highly quality images.
Don't use "Paint". There are many high quality art applications for doing art work. I think even the cell phone apps (Pixlr is pretty good and free!) and web-based image editting apps are better. I use Gimp - free for all platforms.
While a JPEG can't be made transparent in and of itself, if your goal is to reduce the size of very large image areas for the web that need to contain transparent image areas, then there is a solution. It's a bit too complicated to post details, but Google it. Basically, you create your image with transparency and then split out the alpha channel (Gimp can do this easily) as a simple 8-bit greyscale PNG. Then you export the color data as a JPG. Now your web page uses a CANVAS tag to load the JPG as image data and applies the 8-bit greyscale PNG as the Canvas's alpha channel. The browser's Canvas does the work of making the image transparent. The JPEG stores the color info (better compressed than PNG) and the PNG is reduced to 8-bit alpha so its considerably smaller. I've saved a few hundred K per image using this technique. A few people have proposed file formats that embed PNG transparency info into a JPEG's extended information fields, but these proposal's don't have wide support as of yet.
I am successfully using the cool FreeImage library to load images in various formats.
Among these, gif and png with transparency information.
After loading the images, I convert them to 32bpp using FreeImage_ConvertToRawBits. With my png images, this works fine and I can retrieve all four Red/Green/Blue/Alpha components with meaningful Alpha values.
With gif images, on the opposite, the Alpha plane remains all 255's, even though FreeImage_IsTransparent says true.
What am I missing ? Is this related to the fact that gifs are palettized ? How do I handle this ?
I found a clear answer by looking at the source code: transparency is not handled when converting a palettized image to 32 bits. The Alpha field is always set to 255.
Anyway, it is quite possible to retrieve transparency from the original palettized bitmap, pixel by pixel, knowing the value of the transparent color (FreeImage_GetTransparentIndex(dib)).
Which format of PNG should I use PNG 8 or PNG 24? Which one is better for a website. I am confused about these. What is main different between PNG 8 and PNG 2?
Png-24. Png-24 has alpha transparency (where Png-8 only has on/off transparency).
Png-8 is indexed. Png-24 is loss-less.
Png-24 is better in almost every way.
http://www.elated.com/articles/understanding-image-formats/
PNG has several modes which can be used. It may contain:
Greyscale
Indexed colour, usually meant by PNG-8
Greayscale with alpha
Truecolour (RGB)
Truecolour with alpha (RGBA), usually meant by PNG-24
Indexed colour is different from the others that it is a palette of maximum 256 colours, from which indexes are used to denote the colour of specific pixels. It can contain transparency via an auxillary chunk. So every pixel is denoted by a byte-wide value or even less if palette isn't that big. If you use truecolour, there will be more data per pixel, depending on whether you use an alpha-channel.
So in a large image indexed colour will save you a lot of data per each pixel. However, if you use more than 256 colours, some colour data will be lost, which is also more probable in a large image. I would advise to save your image in both formats and see if the loss is worth the gain in smaller file size. Though if you are designing your image for normal web site, not for mobile phones, you should better use PNG-24 anyway, since no one will notice the difference in the size.
I would say that it depends on the image you want to store as PNG*, but in case you've doubts, PNG-24 is better: "true color" (8bits per channel), so that the image must not be dithered and don't "loose" "exact" color match, and optionally PNG-32 if with the alpha channel (transparency) too. PNG-8 images are limited (256 colors chosen from a 24bit palette) and allow only for a mask, you can use it e.g. if you convert from a GIF image; if you convert from other "true color" formats, you "loose" "exact" color match as said (the program try to reduce the real number of used colors into only 256 colors, and other tricks to give resemblance with the original). Some style of icons do not need "true colors", they are "described" well by 256 "fixed" colors or less, and so PNG-8 is ok; as said, if you have GIF images as source, go for PNG-8... if you convert from JPG, go for PNG-24; if you create you image by yourself directly "in" PNG, you know if you can "crunch" the result in PNG-8 or not, but if you are not able to evaluate or use tools to evaluate, PNG-24/32 is ok in any case.
I've written article about it: PNG that works, which outlines all major variants of PNG and their trade-offs/compatibility.
In short, use PNG8 (paletted) whenever you can, as it has much smaller file size. You can have full alpha transparency in PNG8 if you use good tools (Photoshop is not good for PNG).
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When should certain image file types be used when building websites or interfaces, etc?
What are their points of strength and weakness?
I know that PNG & GIF are lossless, while JPEG is lossy.
But what is the main difference between PNG & GIF?
Why should I prefer one over the other?
What is SVG and when should I use it?
If you don't care about each and every pixel, should you always use JPEG since it's the "lightest" one?
You should be aware of a few key factors...
First, there are two types of compression: Lossless and Lossy.
Lossless means that the image is made smaller, but at no detriment to the quality.
Lossy means the image is made (even) smaller, but at a detriment to the quality. If you saved an image in a Lossy format over and over, the image quality would get progressively worse and worse.
There are also different colour depths (palettes): Indexed color and Direct color.
Indexed means that the image can only store a limited number of colours (usually 256), controlled by the author, in something called a Color Map
Direct means that you can store many thousands of colours that have not been directly chosen by the author
BMP - Lossless / Indexed and Direct
This is an old format. It is Lossless (no image data is lost on save) but there's also little to no compression at all, meaning saving as BMP results in VERY large file sizes. It can have palettes of both Indexed and Direct, but that's a small consolation. The file sizes are so unnecessarily large that nobody ever really uses this format.
Good for: Nothing really. There isn't anything BMP excels at, or isn't done better by other formats.
GIF - Lossless / Indexed only
GIF uses lossless compression, meaning that you can save the image over and over and never lose any data. The file sizes are much smaller than BMP, because good compression is actually used, but it can only store an Indexed palette. This means that for most use cases, there can only be a maximum of 256 different colours in the file. That sounds like quite a small amount, and it is.
GIF images can also be animated and have transparency.
Good for: Logos, line drawings, and other simple images that need to be small. Only really used for websites.
JPEG - Lossy / Direct
JPEGs images were designed to make detailed photographic images as small as possible by removing information that the human eye won't notice. As a result it's a Lossy format, and saving the same file over and over will result in more data being lost over time. It has a palette of thousands of colours and so is great for photographs, but the lossy compression means it's bad for logos and line drawings: Not only will they look fuzzy, but such images will also have a larger file-size compared to GIFs!
Good for: Photographs. Also, gradients.
PNG-8 - Lossless / Indexed
PNG is a newer format, and PNG-8 (the indexed version of PNG) is really a good replacement for GIFs. Sadly, however, it has a few drawbacks: Firstly it cannot support animation like GIF can (well it can, but only Firefox seems to support it, unlike GIF animation which is supported by every browser). Secondly it has some support issues with older browsers like IE6. Thirdly, important software like Photoshop have very poor implementation of the format. (Damn you, Adobe!) PNG-8 can only store 256 colours, like GIFs.
Good for: The main thing that PNG-8 does better than GIFs is having support for Alpha Transparency.
PNG-24 - Lossless / Direct
PNG-24 is a great format that combines Lossless encoding with Direct color (thousands of colours, just like JPEG). It's very much like BMP in that regard, except that PNG actually compresses images, so it results in much smaller files. Unfortunately PNG-24 files will still be bigger than JPEGs (for photos), and GIFs/PNG-8s (for logos and graphics), so you still need to consider if you really want to use one.
Even though PNG-24s allow thousands of colours while having compression, they are not intended to replace JPEG images. A photograph saved as a PNG-24 will likely be at least 5 times larger than a equivalent JPEG image, with very little improvement in visible quality. (Of course, this may be a desirable outcome if you're not concerned about filesize, and want to get the best quality image you can.)
Just like PNG-8, PNG-24 supports alpha-transparency, too.
SVG - Lossless / Vector
A filetype that is currently growing in popularity is SVG, which is different than all the above in that it's a vector file format (the above are all raster). This means that it's actually comprised of lines and curves instead of pixels. When you zoom in on a vector image, you still see a curve or a line. When you zoom in on a raster image, you will see pixels.
For example:
This means SVG is perfect for logos and icons you wish to retain sharpness on Retina screens or at different sizes. It also means a small SVG logo can be used at a much larger (bigger) size without degradation in image quality -- something that would require a separate larger (in terms of filesize) file with raster formats.
SVG file sizes are often tiny, even if they're visually very large, which is great. It's worth bearing in mind, however, that it does depend on the complexity of the shapes used. SVGs require more computing power than raster images because mathematical calculations are involved in drawing the curves and lines. If your logo is especially complicated it could slow down a user's computer, and even have a very large file size. It's important that you simplify your vector shapes as much as possible.
Additionally, SVG files are written in XML, and so can be opened and edited in a text editor(!). This means its values can be manipulated on the fly. For example, you could use JavaScript to change the colour of an SVG icon on a website, much like you would some text (ie. no need for a second image), or even animate them.
In all, they are best for simple flat shapes like logos or graphs.
JPEG is not the lightest for all kinds of images(or even most). Corners and straight lines and plain "fills"(blocks of solid color) will appear blurry or have artifacts in them depending on the compression level. It is a lossy format, and works best for photographs where you can't see artifacts clearly. Straight lines(such as in drawings and comics and such) compress very nicely in PNG and it's lossless. GIF should only be used when you want transparency to work in IE6 or you want animation. GIF only supports a 256 color pallete but is also lossless.
So basically here is a way to decide the image format:
GIF if needs animation or transparency that works on IE6(note, PNG transparency works after IE6)
JPEG if the image is a photograph.
PNG if straight lines as in a comic or other drawing or if a wide color range is needed with transparency(and IE6 is not a factor)
And as commented, if you are unsure of what would qualify, try each format with different compression ratios and weigh the quality and size of the picture and choose which one you think is best. I am only giving rules of thumb.
I usually go with PNG, as it seems to have a few advantages over GIF. There used to be patent restrictions on GIF, but those have expired.
GIFs are suitable for sharp-edged line art (such as logos) with a limited number of colors. This takes advantage of the format's lossless compression, which favors flat areas of uniform color with well defined edges (in contrast to JPEG, which favors smooth gradients and softer images).
GIFs can be used for small animations and low-resolution film clips.
In view of the general limitation on the GIF image palette to 256 colors, it is not usually used as a format for digital photography. Digital photographers use image file formats capable of reproducing a greater range of colors, such as TIFF, RAW or the lossy JPEG, which is more suitable for compressing photographs.
The PNG format is a popular alternative to GIF images since it uses better compression techniques and does not have a limit of 256 colors, but PNGs do not support animations. The MNG and APNG formats, both derived from PNG, support animations, but are not widely used.
JPEG will have poor quality around sharp edges etc. and for this reason it is unsuitable for most web graphics. It excels at photographs.
Compared to GIF, PNG offers better compression, larger pallette and more features, including transparency. And it is lossless.
GIF is limited to 256 colors and do not support real transparency. You should use PNG instead of GIF because it offers better compression and features. PNG is great for small and simple images like logos, icons, etc.
JPEG has better compression with complex images like photos.
As of 2018, we have several new formats, better support for previous formats and some clever hacks of using videos instead of images.
For photographs
jpg - still the most widely supported image format.
webp - New format from google. Good potential, though browser support is not great.
For Icons and graphics
svg - whenever possible. It scales well in retina screens, editable in text editors and customisable via JS/CSS if loaded in DOM.
png - if it involves raster graphics (ie when created in photoshop). Supports transparency which is very essential in this use-case.
For Animations
svg - plus css animations for vector graphics. All advantages of svg + power of css animations.
gif - still the most widely supported animated image format.
mp4 - if animated images are actually short video clips. Twitter / Whatsapp converts gifs to mp4.
apng - decent browser support (i.e. no IE, Edge), but creating it is not as straightforward as gifs.
webp - close to using mp4. Poor support
This is a nice comparison of various animated image formats.
Finally, whichever be the format, make sure to optimize it - There are tools for each format (eg SVGO, Guetzli, OptiPNG etc) and can save considerable bandwidth.
There is a hack that can be done to use GIF images to show true color. One can prepare a GIF animation with 256 color paletted frames with 0 frame delay and set the animation to be shown only once. So, all frames could be shown at the same time. At the end, a true colored GIF image is rendered.
Many software is capable of preparing such GIF images. However, the output file size is larger than a PNG file. It must be used if it is really necessary.
Edit: As #mwfarnley mentioned, there might be hiccups. Still, there are still possible workarounds. One may see a working example here. The final rendered image looks like that:
full-color-gif-image
png has a wider color pallete than gif and gif is properitary while png is not. gif can do animations, what normal-png cannot. png-transparency is only supported by browser roughly more recent than IE6, but there is a Javascript fix for that problem. Both support alpha transparency.
In general I would say that you should use png for most webgraphics while using jpeg for photos, screenshots, or similiar because png compression does not work too good on thoose.
GIF based on a palette of 256 colours per image (at least in its basic incarnation). PNG can do "TrueColour", i.e. 16.7 Million colours out of the box. Lossless PNG compresses better than lossless GIFs. GIF can do "binary" transparency (0% opacity or 100% opacity). PNG can handle alpha transparencies.
All in all, if you don't need to use Alpha-transparent images and support IE6, PNG is probably the better choice when you need pixel-perfect images for vector illustrations and such. JPG is unbeatable for photographs.
Here's an updated answer that includes WebP format:
JPEG:
The JPEG file format was created to optimize photos and other images
that use complex color ranges.
When saving a JPEG (e.g. in Photoshop) you can set the optimization level you want to achieve from lossless meaning no detail is lost to extremely lossy.
In most cases for web applications, you can set the compression to
75% without much losing details.
When to use JPEG? Anytime you have a photo or a graphic with complex color gradients and you can't use webP.
PNG
PNG is primarily a lossless bitmap image format for HQ computer generated images.
Unlike a JPEG, it can have a transparent layer. When you see a transparent image or graphic on the web it's usually a PNG.
When to use PNG? Anytime you have a computer generated graphic or an image with transparency. PNG is not recommended for regular photos as
the file size will generally be significantly larger than the
equivalent JPEG or webP.
GIF:
GIF is a 256 color graphic format supporting both images and animations.
Way back, GIFs were often used for simple graphics and then were slowly replaced by JPEG and PNG.
GIF Images: Low file size and low quality. They have almost no colored depth they only have 256 colors to work with. Replace them with SVGs.
Animated GIF: They can become very large very quickly and can potentially create huge performance issues. Replace them with videos. (Twitter for example, converts all animated GIFs that are uploaded into standard video files and then share those video files instead of the animated GIF.)
When to use GIF? For a web application, just don't! Replace GIF images with SVGs; Replace animated GIFs with videos.
SVG
SVG is a web native graphics format describing lines and curves and shapes and allowing the browser to draw the graphics in real time.
SVGs are scalable, meaning the graphic will look good at any size, all the way from tiny to extremely large.
Even CSS can be applied to them.
When to use SVG? Anytime you have a computer generated graphic
that may need to be scaled or needs to be responsive - like an icon, a logo or a graph.
WebP
A brand new lossless and lossy image format with transparency that was created specifically for the web.
It aims to be a replacement for JPEG as it provides good compression with the addition of transparency.
WebP is supported by all modern browsers but have zero support in older browsers so using them right now requires a fallback using an older image format.
When to use webP? For images and computer graphics if you know your
audience will be using newer browsers. If you need to support older
browsers provide fallbacks to either JPEG or PNG.
The main difference is GIF is patented and a bit more widely supported. PNG is an open specification and alpha transparency is not supported in IE6. Support was improved in IE7, but not completely fixed.
As far as file sizes go, GIF has a smaller default color pallet, so they tend to be smaller file sizes at first glance. PNG files have a larger default pallet, however you can shrink their color pallet so that, when you do, they result in a smaller file size than GIF. The issue again is that this feature isn't as supported in Internet Explorer.
Also, because PNGs can support alpha transparency, they're the only option if you want a variation of transparency other than binary transparency.
If you opt for JPEG, and you're dealing with images for a website, you may want to consider the Google Guetzli perceptual encoder, which is freely available. In my experience, for a fixed quality Guetzli produces smaller files than standard JPEG encoding libraries, while maintaining full compatibility with the JPEG standard (so your images will have the same compatibility as common JPEG images).
The only drawback is that Guetzli takes lot of time to encode.. but this is done only once, when you prepare the image for the website, while the benefits remains forever! Smaller images will take less time to download, so your website speed will increase in the everyday use.
GIF has 8 bit (256 color) palette where PNG as upto 24 bit color palette. So, PNG can support more color and of course the algorithm support compression
As pointed out by #aarjithn, that WebP is a codec for storing photographs.
This is also a codec to store animations (animated image sequence). As of 2020, most mainstream browsers has out of the box support for it (compatibility table).
Note for WIC a plugin is available.
It has advantages over GIF because it is based on a video codec VP8 and has a broader color range than GIF, where GIF limits to 256 colors it expands it to 224 = 16777216 colors, still saving significant amount of space.