I am using Matlab's imread to read in images, but about half get read in as all-zeros, even though they are not all-black images (I can view them fine in Finder).
The images that fail vary in their:
file extension (PNG, JPG)
colorspace (RGB, Gray)
color profile (sRGB IEC61966-2.1, Calibrated RGB Colorspace, Generic Gray Gamma 2.2 Profile)
However, I have success reading in other PNG and JPG images in RGB and Gray colorspaces. I don't have any instances of successful reads of an sRGB IEC61966-2.1 color profile, although again, not all images that fail have this profile. I can't see any pattern of file extension, colorspace, etc. that distinguishes that fail from the ones that are read in successfully.
I have tried the following:
[img, map, alpha] = imread('fname.png');. In all cases this produces all-zero matrices for img, map, and alpha.
making the file extension explicit, e.g. imread('fname.png', 'png');. The result is the same.
I am running Matlab 2019b on macOS Catalina.
Any suggestions for what might be causing some images to fail and for how to import them successfully?
The images you linked contain an alpha transparency channel so simply reading using imread() will not return the image data. You need to read the image using additiona parameters as defined on the help page:
[imRGB, map, alpha] = imread('AcbK5pRoi.png');
where the imRGB will contain the RGB image and the Alpha will contain the transparency data.
You can use the imRGB variable as a normal image.
Related
I'm trying to paste an image onto another, using:
original = Img.open('original.gif')
tile_img = Img.open('tile_image.jpg')
area = 0, 0, 300, 300
original.paste(tile_img, area)
new_cropped.show()
This works except the pasted image changes color to grey.
Image before:
Image after:
Is there a simple way to retain the same pasted image color? I've tried reading the other questions and the documentation, but I can't find any explanation of how to do this.
Many thanks
I believe all GIF images are palettised - that is, rather than containing an RGB triplet at each location, they contain an index into a palette of RGB triplets. This saves space and improves download speed - at the expense of only allowing 256 unique colours per image.
If you want to treat a GIF (or palettised PNG file) as RGB, you need to ensure you convert it to RGB on opening, otherwise you will be working with palette indices rather than RGB triplets.
Try changing the first line to:
original = Img.open('original.gif').convert('RGB')
I am using a dataset which provides depth images of human, I need to extract the object from this image or at least remove the other distortion in the image that not belong to the human body In Matlab.
a sample of images is shown below:
This is the output when I used
I = imread ('39.jpg');
human = sum(I,3)>10+10;
human
Any way to do that please?
thanks in Advance
For the image you show, where everything is grayscale but something is red, then just do:
so=imread('https://i.stack.imgur.com/hZOQv.jpg');
human=sum(abs(diff(single(so),1,3)),3)>20;
This essentially compares the difference in RGB values of the pixels, and gets the one above a threshold. If you have proper pngs, then the threshold should just be 1, however with jpg artifacts you may need a higher value, for this image 20 does the job.
There are some tiny artefacts in the result image, very likely due to jpg. When you do science, you need to store in png. If you have absolutely no other choice than jpg, then you may have artefacts.
Is it possible to construct a png image, that is entirely opaque (that means every pixel in the image is opaque) but the image data itself has an alpha channel ?
Why is it that some PNG images don't have an alpha channel ?
Yes. Just like an RGB image may contain only data in the Red channel and not in Green and Blue; "unused" channels are not a problem. Alpha is a separate channel of its own, and in particular, its values should be independent of the associated pixel colors: "PNG does not use premultiplied alpha" (6.2 Alpha representation).
Also see 12.4 Alpha channel creation in the official specifications for some additional details:
The alpha channel can be regarded either as a mask that temporarily hides transparent parts of the image, or as a means for constructing a non-rectangular image. In the first case, the colour values of fully transparent pixels should be preserved for future use. In the second case, the transparent pixels carry no useful data and are simply there to fill out the rectangular image area required by PNG. In this case, fully transparent pixels should all be assigned the same colour value for best compression.
Because they don't need to, per that same specification:
... PNG provides a patent-free replacement for GIF and can also replace many common uses of TIFF. Indexed-color, grayscale, and truecolor images are supported, plus an optional alpha channel. (my emphasis)
The image at the end of this question is a PNG with mode I, which stands for Indexed, as far as I can tell.
I'm trying to create a thumbnail out of it, and save it as JPG with PIL.
However, is I leave the mode alone, PIL won't let me resize it with error unable to generate thumbnail: cannot write mode I as JPEG.
If I convert it to RGB, the result will be a fully white image.
Is there a way to fix this?
https://www.dropbox.com/s/2d1edk2iu4ixk25/NGC281.png
The input image is a 16-bit grayscale PNG, and it appears PIL has a problem with this. Manually converting it to an 8-bit image before further processing makes it work again.
The problem may originate inside PIL itself. The PyPNG homepage asserts
..PIL only has internal representations (PIL mode) for 1-bit and 8-bit channel values. This makes me wonder if PIL can read PNG files with bit depth 2 or 4 (greyscale or palette), and also bit depth 16 (which PNG supports for greyscale and RGB images).
Then again, that page is from 2009. It could be worth tracking down where PIL is maintained from, and report this as a bug (? Or possibly a feature request?).
quick question: I'm creating "random" polygons using either the patch() or the fill() function in Matlab. This works quite good and it is plotted correctly.
However, I need to at least save a few hundres polygons as images to my hard drive for working with them later - so I'm looking for a way to directly save the image in my function rather than saving each polygon myself using the file-menu.
Is there any way to do this?
Thanks in advance!
You can indeed use the print function, but I would not use the jpeg device. JPEG is never the right format for plots (you will get a lot of artifacts near all your lines).
If you need a bitmap image, try the png or tiff device. If you don't need a bitmap, use the appropriate vector image format: fig is the native MATLAB format (which allows you to edit the plot afterwards), so this is the best one if you stick with MATLAB for all your operations. For exporting to other software, I would recommend pdf (works almost anywhere), epsc (EPS with color, great for LaTeX or inkscape), wmf/emf (Windows Metafile, so Windows only, but great for including the images in MS Office). Or you could of course use any of the other formats mentioned in the print documentation.
Sometimes it's a pain in the neck to get the format of your image all right (especially with PDF output). Just take a look at the different properties of your figure and more specifically the PaperSize, PaperUnits and PaperPosition.
The easiest way, and I guess the best solution, is to save as a .fig file. You can do this by using saveas:
h = figure;
% your plot commands here
saveas(h,'mFile.fig');
Afterwards, you can reload the image with the openfig function:
openfig('mFile.fig');
Have to add this answer. This function is helping a lot.
This function saves a figure or single axes to one or more vector and/or bitmap file formats, and/or outputs a rasterized version to the workspace, with the following properties:
- Figure/axes reproduced as it appears on screen
- Cropped/padded borders (optional)
- Embedded fonts (pdf only)
- Improved line and grid line styles
- Anti-aliased graphics (bitmap formats)
- Render images at native resolution (optional for bitmap formats)
- Transparent background supported (pdf, eps, png)
- Semi-transparent patch objects supported (png only)
- RGB, CMYK or grayscale output (CMYK only with pdf, eps, tiff)
- Variable image compression, including lossless (pdf, eps, jpg)
- Optionally append to file (pdf, tiff)
- Vector formats: pdf, eps
- Bitmap formats: png, tiff, jpg, bmp, export to workspace