It seems that ghostscript uses different device for PNG24 and grayscale.
Is there a way to convert an EPS file to PNG24 format that is grayscale?
I actually wanted to remove the colorspace of the image. However, which colorspace type should I use in the transformimagecolorspace method COLORSPACE_UNDEFINED or any thing else?
I am using OpenCV 3.0 and whenever I read an image and write it back the result is a washed-out image.
code:
cv::Mat img = cv::imread("dir/frogImage.jpg",-1);
cv::imwrite("dir/result.jpg",img);
Does anyone know whats causing this?
Original:
Result:
You can try to increase the compression quality parameter as shown in OpenCV Documentation of cv::imwrite :
cv::Mat img = cv::imread("dir/frogImage.jpg",-1);
std::vector<int> compression_params;
compression_params.push_back(CV_IMWRITE_JPEG_QUALITY);
compression_params.push_back(100);
cv::imwrite("dir/result.jpg",img, compression_params);
Without specifying the compression quality manually, quality of 95% will be applied.
but 1. you don't know what jpeg compression quality your original image had (so maybe you might increase the image size) and 2. it will (afaik) still introduce additional minor artifacts, because after all it is a lossy compression method.
UPDATE your problem seems to be not because of compression artifacts but because of an image with Adobe RGB 1998 color format. OpenCV interprets the color values as they are, but instead it should scale the color values to fit the "real" RGB color space. Browser and some image viewers do apply the color format correctly, while others don't (e.g. irfanView). I used GIMP to verify. Using GIMP you can decide on startup how to interpret the color values by format, either getting your desired or your "washed out" image.
OpenCV definitely doesn't care about such things, since it's not a photo editing library, so neither on reading nor on writing, color format will be handled.
This is because you are saving the image as JPG. When doing this the OpenCV will compress the image.
try to save it as PNG or BMP and no difference will be exist.
However, the IMPORTANT QUESTION : I am loading the image as jpg and saving it as JPG. So, how there is a difference?!
Yes, this is because there is many not identical compression/decompression algorithms for JPG.
if you want to get into some details see this question:
Reading jpg file in OpenCV vs C# Bitmap
EDIT:
You can see what I mean exactly here:
auto bmp(cv::imread("c:/Testing/stack.bmp"));
cv::imwrite("c:/Testing/stack_OpenCV.jpg", bmp);
auto jpg_opencv(cv::imread("c:/Testing/stack_OpenCV.jpg"));
auto jpg_mspaint(cv::imread("c:/Testing/stack_mspaint.jpg"));
cv::imwrite("c:/Testing/stack_mspaint_opencv.jpg", jpg_mspaint);
jpg_mspaint=(cv::imread("c:/Testing/stack_mspaint_opencv.jpg"));
cv::Mat jpg_diff;
cv::absdiff(jpg_mspaint, jpg_opencv, jpg_diff);
std::cout << cv::mean(jpg_diff);
The Result:
[0.576938, 0.466718, 0.495106, 0]
As #Micha commented:
cv::Mat img = cv::imread("dir/frogImage.jpg",-1);
cv::imwrite("dir/result.bmp",img);
I was always annoyed when mspaint.exe did the same to jpeg images. Especially for the screenshots...it ruined them everytime.
I'm currently building a site in app engine that uploads images to google cloud storage and to complete basic manipulations I'm using python's PIL
I've been having problems with the following image which another stackoverflow member has mentioned is a palette-based PNG with transparency, which I've been reading may be a bit buggy in PIL
My question is really a back to basics one: What is the best way to convert this to an RGB format with transparent pixels set to #FFF? I've been able to get it to work through a combined RGBA then RGB paste but that seems redundant
However, for a direct conversion I'm getting a bad transparency mask i.e. using the solution from PIL Convert PNG or GIF with Transparency to JPG without
Also if anybody has ideas why the image degrades to terrible quality after conversion, that's entirely a bonus for me!
A way to do this is to first convert the file to jpg -- seems like a problem with the png encoding (or something related to that)
Check out this link that I used and got smooth conversion from transparent PNG to GIF:
Convert RGBA PNG to RGB with PIL
The function you are looking for is pure_pil_alpha_to_color_v2.
I also used for my image conversion tool PySmile:
https://github.com/vietlq/PySmile/blob/master/pysmile.py
I would like to be able to use the cpselect matlab tool (or a similar one) with the capability of showing both images (moving image and reference image) in RGB (I only managed to see moving image in RGB and reference image in grayscale).
Could someone point me to an alternative for this tool that would support this or anyway to be able to display both image in rgb in cpselect?
Thanks in advance.
Not sure what you're talking about, and I'm quite confused about your statement. cpselect is image independent. You can show both of them as colour or grayscale or one or the other. The example you're probably looking at is the one that comes with MATLAB: http://www.mathworks.com/help/images/ref/cpselect.html . One image is grayscale, while the other has a pinkish hue.
Here's an example showing both the source and target image as being in colour. I used onion.png that is a colour image that is part of the MATLAB system path:
im = imread('onion.png');
im_rotate = imrotate(im, 35);
cpselect(im, im_rotate);
We get: