I have a 2-pixel PNG image with the following rgba:
image.setAt(0, 0, { red:255, green:10, blue:10, alpha:100 });
image.setAt(1, 0, { red:255, green:255, blue:55, alpha:255 });
image.setAt(0, 1, { red:90, green:10, blue:65, alpha:250 });
image.setAt(1, 1, { red:60, green:255, blue:0, alpha:14 });
(using node's pngjs-image module)
When the image is loaded by the browser (firefox) and copied to canvas to test the rgba data, the following is returned:
255 7 7 100
255 255 55 255
89 9 64 250
54 255 0 14
It seems like only Alpha channel values are preserved while pixel colors are arbitrarily changed.
What's going on?
(using Firefox 41 on Linux)
EDIT
From intro on pngtoy nodejs module I have found the following:
Low-level implementation of PNG file parser/reader/decoder using
JavaScript on client size.
Why this when browsers support PNG already?
The browser will simply load and convert any PNG type into RGBA
bitmaps. It will also apply ICC and gamma correction to the image
resulting in different values than in the original bitmap.
However, I thought that PNG itself should have ICC and Gamma correction chunks so that the browser applies them. Does the browser make such image manipulation to any png file even without ICC/gamma chunk inside the file?
Firefox converts images with alpha to pre-multiplied alpha for internal use. If your workflow is recovering the image from Firefox' internal image buffer, there will be loss of precision when reversing the pre-multipled alpha. In the extreme, pixels with alpha equal to zero will be returned as transparent black, regardless of the underlying color in the original PNG. This effect doesn't depend upon whether color management chunks are present or not.
Note that this doesn't happen when you click on a PNG image and "save as..."; in this case the original PNG is returned.
Firefox may also modify the internal image (depending upon the setting of gfs.color_management.mode in "about:config") when color management chunks (iCCP, sRGB, gAMA, and/or cHRM) are present, but that does not seem to be the case for this particular question. Again, "save as..." will return the original pixels and the color management chunks unchanged.
Related
I've got an RTF file with an embedded image in it. The image is scaled by 2/3, or 0.67. It displays correctly in Word, but when the file is printed it consistently displays by ignoring the scale setting.
The source image is a PNG with dimensions 297x117 (pixels). The image was originally encoded as follows:
{\pict\pngblip\picw7858\pich3096\picwgoal4455\pichgoal1755\picscalex67\picscaley67
<Hex-encoded PNG image>}
The original picture width/height is calculated as (w,h) * 2.54 * 1000 / 96 (twips).
The original picture width/height goal is calculated as (w,h) * 1440 / 96 (twips).
A twip is 1/1440 inch and 2.54 is the number of centimetres in an inch.
I edited it to try setting the size manually. I multiplied all of these values by 2/3 and removed the \picscale[xy]67 instructions:
{\pict\pngblip\picw5239\pich2064\picwgoal2985\pichgoal1176
<Hex-encoded PNG image>}
However, it still seems to only use the size of the PNG (297x117) when printing it. The screen display and the print result both appear unchanged from before.
Other than manually rescaling the image and re-embedding it into the RTF, can I get the printed version to respect the scaling?
UPDATE
I did try embedding an image resized to 2/3 of the previous dimensions, but the printed image is still 50% larger than the on-screen image (the extra area gets cropped). The only difference is that it was much lower resolution.
I also tried the same image in a Word document and it printed perfectly, so it's definitely a difference between .docx and .rtf files. Is it perhaps a dpi setting in the PNG image?
Windows 10 updated itself last night, and now I can't replicate the problem. All old files that previously had this problem, no longer have this problem. Go Microsoft!
It appears to be this update that resolved the issue: https://support.microsoft.com/en-au/help/4093112/windows-10-update-kb4093112
Addresses an issue with printing content generated by ActiveX in Internet Explorer
There's no more information about this, but it is related to printing.
I am working on a website right now. Sadly the png logo and as well the background which uses the same colors is displayed on some computers with Firefox in lila. With Chrome the blue looks as expected.
The used monitor also has an effect, but with Chrome everything looks fine.
Where does that issue come from, and how can I fix that?
Here is my image
Here you see a photo of my monitor. The lila with firefox (on the left) is visible slightly. The big issue is that the color is used in the background of my website, which looks lila than, with firefox, and the displayed color does not match the other colors in css at my website anymore.
The above picture is from firefox:
The above picture is from chrome:
Firefox handles images that contain an sRGB profile slightly differently from untagged images and HTML colors, by default. It has three modes of operation that you can select by going to "about:config", searching for gfx.color_management.mode. The default is "2". Change it to "0" (no color management) or "1" (color manage everything) and you'll get a good match.
See the four-year-old bug #621474 at https://bugzilla.mozilla.org and scroll down to comment #49 to see current status of the patch.
Because of these differences (you can't control which setting people use), it's probably best to just remove the iCCP chunk or sRGB chunk from your image. Browsers will assume the image is in the sRGB colorspace and display it properly against HTML colors.
"pngcheck" says you have iCCP and cHRM chunks:
$ pngcheck -v so-logo.png
File: so-logo.png (147985 bytes)
chunk IHDR at offset 0x0000c, length 13
506 x 171 image, 32-bit RGB+alpha, non-interlaced
chunk pHYs at offset 0x00025, length 9: 2835x2835 pixels/meter (72 dpi)
chunk iCCP at offset 0x0003a, length 2639
profile name = Photoshop ICC profile, compression method = 0 (deflate)
compressed profile = 2616 bytes
chunk cHRM at offset 0x00a95, length 32
White x = 0.31269 y = 0.32899, Red x = 0.63999 y = 0.33001
Green x = 0.3 y = 0.6, Blue x = 0.15 y = 0.05999
chunk IDAT at offset 0x00ac1, length 145212
zlib: deflated, 32K window, maximum compression
chunk IEND at offset 0x24209, length 0
No errors detected in so-logo.png (6 chunks, 57.2% compression).
There are various tools you can use to remove those chunks:
pngcrush (also removes the pHYs chunk):
pngcrush -rem alla -force logo.png logo_crushed.png
pngsplit+cat:
pngsplit logo.png
rm logo.png.0003.iCCP
rm logo.png.0004.cHRM
cat logo.png.00*.* > logo_split_cat.png
PNG files include ICC color profile metadata. Some browsers ignore this metadata and display the image as if its bits represent an sRGB image. Other browsers take into account the ICC colorspace and make the appropriate color transformations before outputting to the display. If the PNG uses the sRGB color profile, it should look the same in all browsers. However, if your PNG has some other color profile (such as AdobeRGB), then perhaps Firefox is not compensating whereas Chrome is. In this case, the Firefox image is technically displayed incorrectly, although it will match RGB font colors in your HTML, whereas the Chrome image is displayed "correctly" (i.e. to the creator's original intent for the colors) but will not match the RGB font colors in your HTML (which are specified in sRGB).
Bottom line, check the ICC colorspace of your PNG.
I have a report that renders images (jpg) that have been collected from various sources. This works fine within the report viewer, and when exporting via Excel.
However, when exporting to PDF, about 5% of the images are rendered incorrectly as can be seen below, with the original on the left, and what is rendered on the right;
I find that if I open up one of these images in mspaint, and just click save, on the next report-run the image is now rendered correctly.
Are there any rules as to what image properties/format are valid for SSRS to render the image correctly within a PDF? Essentially I'd like to somehow find these images that will render incorrectly before the report is run and fix them prior...
Current Workaround
I never ended up getting SSRS to display the the problem images as they were, however, determining before running the report which images would be included in the non-displayable set so they could be converted to a supported format (automatically) was also a solution.
In my case, all images were supplied via users uploading to a website, so I was able to identify and convert images as they arrived. For all existing images, I was able to run a script that identified the problem images and convert them.
Identifying problem images
From the thousands of images I had, I was able to determine that the images that wouldn't render correctly had the following properties:
Image had CMYK colorspace or;
Image had extended color profiles or;
Both of the above
Converting an image
I was originally using the standard .NET GDI (System.Drawing) to manipulate images however the API is often prone to crashes (OutOfMemoryException) when dealing with images that have extra data. As such, I switched to using ImageMagick where for each of the identified images I:
Stripped the color profiles and;
Converted to RGB
Note that the conversion to RGB from CMYK without stripping the color profiles was not enough to get all images to render properly.
I ended up just doing those items on every image byte stream I received from users (without first identifying the problem) before saving an uploaded image to disk. After which, I never had the rendering problem again.
Because of the way the output looks I would say those JPEG images have CMYK colorspace but the SSRS assumes they use RGB colorspace and sets the wrong colorspace in PDF.
If you can post a JPEG image and a sample PDF I can give you more details.
I've had exactly the same problem with an image rendering correctly on screen but appearing like the one in the question when I exported the report to PDF. Here's how I solved it.
The Problem
The first clue was this article I came across on MSDN. It seems that regardless of the original image density, the PDF renderer in SSRS resizes all images to 96 DPI. If the original size of the image is larger than the size of the page (or container), then you will get this problem.
The Solution
The solution is to resize the source image such that it will fit on your page. The requires a little calculation depending on your page size and margin settings.
In my case, I'm using A4 paper size, which is 21cm by 29.7cm. However, my left margin is 1.5cm, and my right margin is 0.5cm, for a total inner width of 19cm. I allow an extra 0.5 cm as a margin of error, so I use an inner width of 18.5cm.
21 cm - 1.5 cm - 0.5 cm - 0.5 cm = 18.5 cm
As noted before, the resolution generated by the PDF renderer is 96 DPI (dots per inch). For those of us not in the United States or Republic of Liberia, that's 37.79 DPC (dots per centimetre). So, to get our width:
18.5 cm * 37.79 dpc = 699 pixels
Your result may be different depending on (1) the paper size you are using, and (2) the left and right margins.
As the page is higher than it is wide, we need only resize the width while keeping the image proportional. If you're using a paper size which is wider than it is tall, you'd use the length instead.
So now open the source image in Paint (or your image editor of choice), and proportionally resize the image to the desired width (or length) in pixels, save it, import it into your container, and size the image visually with respect to the container. It should look the same on screen, and now render correctly to PDF.
This is an issue reported to Microsoft Connect.
From SSRS 2008 How to get the best image quality possible?:
The image behavior you see in PDF is a result of some image conversions that the PDF renderer does, based on how the PDF specification requires that serialize images into PDF.
We know it's not ideal, and we classify the loss of image quality as a product issue. Therefore, it's difficult to really say what to do to get the best quality image.
Anecdotally, I have heard that customers have good results when the original image is a BMP
I'm having trouble viewing a file that is declared to be a TIFF HDR image by Hugin.
Windows Explorer "Properties => Details" states that the bit-depth of the image is 128
Windows Explorer shows it as a white image.
I've tried converting the image to JPEG via ImageMagick, white image.
Picasa Image Viewer says "Invalid image".
I've tried opening it in Photoshop CS5, white image.
These are the stiching options set in Hugin; http://i.imgur.com/vmzA9.png
These is the Images tab in Hugin; http://i.imgur.com/33ySq.png
This is the entire output of Hugin; http://i.imgur.com/smV6O.png
Here is the complete TIFF _hdr file; http://c759972.r72.cf0.rackcdn.com/DSC_3873-DSC_3875_hdr.tif Size: 64 MB
So, is the problem that I'm not viewing it in the correct mode -- or that it really is a white image?
I imported your image using Mathematica. After import, it appears white. That is because the pixel values are not scaled properly: The maximum value is 1070 whereas any value greater than 1 is displayed as white. When rescaling the values to run in the range from 0 to 1, one can see the following:
In[64]:= image = Import["http://c759972.r72.cf0.rackcdn.com/DSC_3873-DSC_3875_hdr.tif"];
In[65]:= ImageType[image]
Out[65]= "Real32"
In[66]:= Max[ImageData[image]]
Out[66]= 1070.
In[67]:= ImageAdjust[image]
Either the image file is indeed corrupted, or the various programs can't read it. Anyway, the image is not white. There seems also to be some mis-alignment between the poses that were used to create the HDR.
Here is an image:
This image is a simple black-to-transparent gradient saved in full RGBA PNG.
Here is the same image, converted to indexed-alpha PNG by GIMP (Photoshop produces the same result)
As you can see, the gradient is now half-opaque, half-transparent.
Here is the same image again, only this time it was converted to indexed-alpha PNG by a PHP script I wrote:
So my question is: Why are GIMP and Photoshop unable to support partial transparency in indexed images, when the PHP script clearly shows that such an image can be created with no problems?
Is there anything "wrong" with an image whose pallette contains alpha information?
A more programming-related question: Does this transparency in the last image work in Internet Explorer 6?
I've finally found the actual answer: There is a metadata entry that allows you to define the alpha value of each colour in the colour table. Most graphics programs don't make use of this, but it does exist and can be used, in particular by GD.
Another option besides fireworks is pngquant, a command line application that will convert a rgba png into an indexed png with transparency.
I found this post which talks some more about how to use it.
IE6 and earlier in windows does not support variable transparency PNGs without annoying workarounds. An indexed PNG will only show the fully opaque parts which usually works pretty well. A drop shadow would disappear but the opaque parts of the logo or icon would continue to show.
This page has a better explanation and instructions with more png compression and quantization tools: http://calendar.perfplanet.com/2010/png-that-works/
For the record, PNG does not literally support indexed images with an alpha channel. What is really happening is that PNG allows you to add additional colors to the color table (i.e. index) with alpha values in those colors... not a complete alpha channel. FWIW...
Yeah I know what you mean. Fireworks is the only image editing program that I know of that can create and edit PNG8+Alpha without problems. I wish more paint programs would support this format cause Fireworks is expensive!
I found a way in GIMP to create or convert an image with reduced color palette and alpha channel.
The trick is to add a mask to the layer.
Full steps to reproduce:
Have your image in one layer
Add a mask to the layer. Select Transfer layer's alpha channel.
Convert to Indexed (Image -> Mode -> Indexed...)
Save as PNG
Now your image has reduced colors and reduced size, but it keeps your smooth transparency.