How can I accomplish this? A programmatic solution (Objective-c) is great, but even a non-progarmmatic one is good.
I have pixelmator -> But that doesn't give you the option. I can't seem to do it with Preview either.
I have tried googling, but haven't been able to find a solution so far. The only tool I have been able to use to do this is TexturePacker, but that creates a sprite sheet.
You can use libpng to convert the PNG image to three-byte (8:8:8) RGB. Then you can downsample to the 5:6:5 16-bit color values of RGB565. If r, g, and b are the respective 8-bit colors (stored in an unsigned char type), then the 16-bit RGB565 value is:
((r >> 3) << 11) | ((g >> 2) << 5) | (b >> 3)
You can improve a tad on this by rounding instead of chopping, being careful to not overflow the values. You can also force the green value to be equal to the blue and red values when they are all equal in the original 8-bit values. Otherwise it is possible to have colors that were originally gray inadvertently take on color after conversion.
Create Bitmap Context with color RGB565 using Quartz, paint your PNG on this context, save this bitmap context to file.
PNG does not support a RGB565 packing. You can always apply a posterize to the image (programatically or with ImageMagick or with any image editor), which amounts to discard the lower significant bits in each channel. When saving to PNG, you will still be saving 8 bits per channel (unless you use a palette), but even then you will get an appreciable reduction in size, because of the PNG compression.
A quick example: original:
after a simple posterize with 32 levels (equivalent to a RGB555) applied with XnView
The size goes from 89KB to 47KB, with a small quality loss.
In case of synthetic images with gradients, the quality loss could be much more noticiable (banding).
I received this answer from the creator of texture packer:
you can do it from command line - see
http://www.texturepacker.com/uncategorized/batch-converting-images-to-pvr-or-pvr-ccz/
Just adjust the opt and set output to .png instead of pvr.ccz
Make sure that you do not overwrite your source images.
According to Wikipedia, which is always right, the only 16-bit PNG is a greyscale PNG. http://en.wikipedia.org/wiki/Portable_Network_Graphics
If you just add your 32-bit (alpha) or 24-bit (no alpha) PNG to your project as normal, and then set the texture format in Cocos2D, all should be fine. The code for that is:
[CCTexture2D setDefaultAlphaPixelFormat:kCCTexture2DPixelFormat_RGB565];
Related
I use vkGetPhysicalDeviceSurfaceFormatsKHR to get supported image formats for the swapchain, and (on Linux+Nvidia, using SDL) I get VK_FORMAT_B8G8R8A8_UNORM as the first option and I go ahead and create the swapchain with that format:
VkSwapchainCreateInfoKHR swapchain_info = {
...
.imageFormat = format, /* taken from vkGetPhysicalDeviceSurfaceFormatsKHR */
...
};
So far, it all makes sense. The image format used to draw on the screen is the usual 8-bits-per-channel BGRA.
As part of my learning process, I have so far arrived at setting up a lot of stuff but not yet the graphics pipeline1. So I am trying the only command I can use that doesn't need a pipeline: vkCmdClearColorImage2.
The VkClearColorValue used to define the clear color can take the color as float, uint32_t or int32_t, depending on the format of the image. I would have expected, based on the image format given to the swapchain, that I should give it uint32_t values, but that doesn't seem to be correct. I know because the screen color didn't change. I tried giving it floats and it works.
My question is, why does the clear color need to be specified in floats when the image format is VK_FORMAT_B8G8R8A8_UNORM?
1 Actually I have, but thought I would try out the simpler case of no pipeline first. I'm trying to incrementally use Vulkan (given its verbosity) particularly because I'm also writing tutorials on it as I learn.
2 Actually, it technically doesn't need a render pass, but I figured hey, I'm not using any pipeline stuff here, so let's try it without a pipeline and it worked.
My rendering loop is essentially the following:
acquire image from swapchain
create a command buffer with the following:
transition from VK_IMAGE_LAYOUT_UNDEFINED to VK_IMAGE_LAYOUT_GENERAL (because I'm clearing the image outside a render pass)
clear the image
transition from VK_IMAGE_LAYOUT_GENERAL to VK_IMAGE_LAYOUT_PRESENT_SRC_KHR
submit command buffer to queue (taking care of synchronization with swapchain with semaphores)
submit for presentation
My question is, why does the clear color need to be specified in floats when the image format is VK_FORMAT_B8G8R8A8_UNORM?
Because the normalized, scaled, or sRGB image formats are really just various forms of floating-point compression. A normalized integer is a way of storing floating-point values on the range [0, 1] or [-1, 1], but using a much smaller amount of data than even a 16-bit float. A scaled integer is a way of storing floating point values on the range [0, MAX] or [-MIN, MAX]. And sRGB is just a compressed way of storing linear color values on the range [0, 1], but in a gamma-corrected color space that puts precision in different places than the linear color values would suggest.
You see the same things with inputs to the vertex shader. A vec4 input type can be fed by normalized formats just as well as by floating-point formats.
I'm using imagemagick to create an animated GIF out of ~60 JPG 640x427px photos. The combined size of the JPGs is about 4MB.
However, the output GIF is ~12MB. Is there a reason why the GIF is considerably bigger? Can I conceivably achieve a GIF size of ~4MB?
The command I'm using is:
convert -channel RGB # no improvement in size
-delay 2x10 \
-size 640 \
-loop 0 \
-dispose Background # no improvement in size
-layers Optimize # about 2MB improvement
portrait/*.jpg portrait.gif
Using gifsicle didn't seem to improve either.
JPG is lossy compression.
GIF is lossless compression.
A better comparison would be to convert all the source images to GIF first, then combine them..
First google hit for GIF compression is http://ezgif.com/optimize which claims lossy GIF compresion, might work for you but I offer no warranty as I haven't tried it.
JPEG achieves it's compression through a (lossy) transform, where an 16x16 / 8x8 block of pixels is transformed to frequency representation and then quantized. Instead of selecting e.g. 256 levels (i.e. 8 bits) of red/green/blue per component, JPEG can ignore some frequency components, or use just 1 or 2 bits to represent them.
GIF on the other hand works by identifying repeated patterns from a paletted image (upto 256 entries), which occur exactly in the previously encoded/decoded stream. Both because of the JPEG compression, and the source of the images typically encoded by JPEG (natural full color), the probability of (long) exact matches is quite low.
60 RGB images with the size 640x427 is about 16 million pixels. To represent that much in 4 MB, requires a compression of 2 bits per pixel. To achieve this with GIF would require a very lossy algorithm, that would select (vector) quantization of true color pixels not to the closest pixel in the target GIF palette, but based also on the fact how good dictionary of code words this particular selection will make. The dictionary builds slowly and to achieve 2 bits/pixel, the average length of the decoded code word would have to map to 5.5 matching pixels in the close neighborhood.
By contrast, imagemagick has been able to compress the 16 million pixels (each selected from a palette of 256 elements) to 75% already!
my code to save bmp format:
ImgResult.Save(dlgSavePicture.FileName, System.Drawing.Imaging.ImageFormat.Bmp)
I have tried the code and the output is a 512x512 bmp image with 1 megabyte size
if i use ms paint to create a 515x512 bmp image, the size is 768kb
i have tried to open the image and resave as bmp and the size still 1MB
can a 512x512 bmp image size upto 1mb in 512x512? or there are something wrong with my code?
BMP is a very simple image file format. Just a little header that describes the image (size, pixel format, resolution, color table), followed by a blob of pixel data. Technically it can be compressed with RLE but encoders don't bother anymore. The pixel data depends on the pixel format, ancient ones are 1bpp, 4bpp and 8bpp, they require a color table. 16bpp can happen, unusual, normal ones are 24bpp (RGB) and 32bpp (ARGB). In other words, 3 or 4 bytes per pixel.
So yes, 512 x 512 x 4 ~= 1 megabyte. MSPaint is pretty explicit about the pixel format it uses. It is a very simple painting program without support for alpha blending effects. So uses 24bpp (no alpha), 512 x 512 x 3 ~= 786 kilobytes. You could use Paint.NET to create 32bpp BMPs.
Which one you get in your own program depends on how you created the Bitmap object. The simple version uses the same pixel format as the video adapter. On all modern machines that's 32bpp. 16bpp can happen, it is very unusual. If you want another format then you have to use the Bitmap constructor that takes a PixelFormat argument.
There's otherwise a pretty good reason to do this, the default pixel format is not usually the most optimal one. The best one by a factor of 10 is the format that matches the pixel format of the video adapter exactly. Choice is between 32bppArgb and 32bppPArgb. The P means "pre-multiplied", the alpha value is applied to the RGB values up front. Argb is most efficient if you do a lot of drawing into the bitmap yourself with Graphics.FromImage(). PArgb is most efficient for painting, the pixel data can be blitted to the video frame buffer directly without having to be converted. Ten times faster. You usually care about painting speed, the most visible artifact of a program.
If you care about image file size then there is no better choice than PNG. It compresses the pixel data with LZW compression, typical compression rates are 50% or better. JPEG is a decent choice as well, much higher compression rates, but it is lossy. It achieves high rates by throwing away image details. Suitable for photos, in general images without text or line art, that don't otherwise have to be compressed multiple times.
i have tried this code
Public Function ConvertTo24bpp(img As Image) As Bitmap
Dim bmp = New Bitmap(img.Width, img.Height, System.Drawing.Imaging.PixelFormat.Format24bppRgb)
Using gr = Graphics.FromImage(bmp)
gr.DrawImage(img, New Rectangle(0, 0, img.Width, img.Height))
End Using
Return bmp
End Function
ImgResult = New Bitmap(Original)
For j = 0 To Original.Height - 1
For i = 0 To Original.Width - 1
ImgResult.SetPixel(i, j, Color.FromArgb(resultArray2(j, i, 0), originalArray(j, i, 1), resultArray2(j, i, 2)))
Next
Next
Dim clone As Bitmap
clone = ConvertTo24bpp(ImgResult)
clone.Save(dlgSavePicture.FileName)
the output is 24bit 512x512 bmp image but it size is ~640 KB not ~678 KB
i think the output is png format with bmp extension
is my code gone wrong?
I have many scanned document in PDF.
I use ImageMagick with Ghostscript to convert PDF to PNG in big density. I use convert -density 288 2.pdf 2.png. After that I read the pixels with PHP and find where is QR code and decode it. Because image is very big (~ 2500px), it's need very much RAM. I want, before I read pixels with PHP, to crop the image with ImageMagick and leave only that part with the QR code.
Can I detect the approximate location of QR code with ImageMagick, crop and leave only that part ?
Sample PDF
Converted PNG
Further Update
I see your discussion with Kurt about better extraction of the image from the PDF in the first place, and his recommendation was to use pdfimages. I just wanted to add that you won't find that if you do brew search pdfimages, but you actually need to use
brew install poppler
and then you get the pdfimages executable.
Updated Answer
If you change the tile size to 100x100 on the crop command and run this for the second PDF you supplied:
convert -density 288 pdf2.pdf -crop 100x100 tile%04d.png
and then use the same entropy analysis command
convert -format "%[entropy]:%X%Y:%f\n" tile*.png info: | sort -n
...
...
0.84432:+600+3100:tile0750.png
0.846019:+600+2800:tile0678.png
0.980938:+700+400:tile0103.png
0.984906:+700+500:tile0127.png
0.988808:+600+400:tile0102.png
0.998365:+600+500:tile0126.png
The last 4 listed tiles are
Likewise for the other PDF file you supplied, you get
0.863498:+1900+500:tile0139.png
0.954581:+2000+500:tile0140.png
0.974077:+1900+600:tile0163.png
0.97671:+2000+600:tile0164.png
which means these tiles
I would think that should help you pretty much approximately locate the QR code.
Original Answer
This is not all that scientific, but it may help you get started. The key, I think, is the entropy of the various areas of the image. The QR code has a lot of information encoded in a small area so it should have high entropy. So, I use ImageMagick to split the image into square 400x400 tiles like this:
convert image.png -crop 400x400 tile%03d.png
which gives me 54 tiles. Then I calculate the entropy of each of the tiles and sort them by increasing entropy, also outputting their offsets from the top left of the frame, and their name, like this:
convert -format "%[entropy]:%X%Y:%f\n" tile*.png info: | sort -n
0.00408949:+1200+2800:tile045.png
0.00473755:+1600+2800:tile046.png
0.00944815:+800+2800:tile044.png
0.0142171:+1200+3200:tile051.png
0.0143607:+1600+3200:tile052.png
0.0341039:+400+2800:tile043.png
0.0349564:+800+3200:tile050.png
0.0359226:+800+0:tile002.png
0.0549334:+800+400:tile008.png
0.0556793:+400+3200:tile049.png
0.0589632:+400+0:tile001.png
0.0649078:+1200+0:tile003.png
0.10811:+1200+400:tile009.png
0.116287:+2000+3200:tile053.png
0.120092:+800+800:tile014.png
0.12454:+0+2800:tile042.png
0.125963:+1600+0:tile004.png
0.128795:+800+1200:tile020.png
0.133506:+0+400:tile006.png
0.139894:+1600+400:tile010.png
0.143205:+2000+2800:tile047.png
0.144552:+400+2400:tile037.png
0.153143:+0+0:tile000.png
0.154167:+400+400:tile007.png
0.173786:+0+2400:tile036.png
0.17545:+400+1600:tile025.png
0.193964:+2000+400:tile011.png
0.209993:+0+3200:tile048.png
0.211954:+1200+800:tile015.png
0.215337:+400+2000:tile031.png
0.218159:+800+1600:tile026.png
0.230095:+2000+1200:tile023.png
0.237791:+2000+0:tile005.png
0.239336:+2000+1600:tile029.png
0.24275:+800+2400:tile038.png
0.244751:+0+2000:tile030.png
0.254958:+800+2000:tile032.png
0.271722:+2000+2000:tile035.png
0.275329:+0+1600:tile024.png
0.278992:+2000+800:tile017.png
0.282241:+400+1200:tile019.png
0.285228:+1200+1200:tile021.png
0.290524:+400+800:tile013.png
0.320734:+0+800:tile012.png
0.330168:+1600+2000:tile034.png
0.360795:+1200+2000:tile033.png
0.391519:+0+1200:tile018.png
0.421396:+1200+1600:tile027.png
0.421421:+2000+2400:tile041.png
0.421696:+1600+2400:tile040.png
0.486866:+1600+1600:tile028.png
0.489479:+1600+800:tile016.png
0.611449:+1600+1200:tile022.png
0.674079:+1200+2400:tile039.png
and, hey presto, the last one listed (i.e. the one with the highest entropy) tile039.png is this one.
I have drawn a rectangle around its location using this command
convert image.png -stroke red -fill none -strokewidth 3 -draw "rectangle 1200,2400 1600,2800" a.jpg
I concede there may be luck involved, but I only have one image to test my mad theories. You may need to tile twice, the second time with an x-offset and y-offset of half a tile width, so that you don't cut the QR code and split it across 2 tiles. You may need different size tiles for different size barcodes. You may need to consider the last 3-5 tiles located for your next algorithm. But I think it could form the basis of a method.
i want to shrink png or jpg on OSX. i only want to shrinkg without affecting the image quality.
like tinypng.org
is there any recommended library? i just know imagemagick. is there a way to do that natively? or another library to shrink/compress images without affecting the image quality?
my aim is to shrink the file size, for example:
logo.png >> 476 k before shrink
logo.png >> 50k after shrink
Edit: to be clear, i want to compress the size of the file, not the image resolution.
TinyPNG.org works by using image quantisation - the similar colours in the image are converted into a HSV or RGB model and then merged depending on the distance.
How does it work?
...
When you upload a PNG (Portable Network Graphics) file, similar colours in your image are combined. This technique is called “quantisation”
...
src: http://tinypng.org
An answer here outlines a method of doing so: https://stackoverflow.com/a/492230/556479.
There are also some answers on this question with refer to how you can do so on Mac OS using objective-c: How do I reduce a bitmap to a known set of RGB colours
See Wikipedia for a more in depth guide: http://en.wikipedia.org/wiki/Color_quantization
Did you have a problem using ImageMagick? It has a rich set of quantize functions such as
bool MagickQuantizeImage( MagickWand mgck_wnd,
float number_colors,
int colorspace_type,
float treedepth,
bool dither,
bool measure_error )
Here is a very thorough guide to quantization using imageMagick
My suggestion is to use http://pngnq.sourceforge.net, it will give better results than ImageMagick and for the single example given in http://tinypng.org, it also produces a very similar output. It is a tiny C implementation of the method present in the paper "Kohonen Neural Networks for Optimal Colour Quantization". That alone is much better since you are no longer relying on closed unknown implementations.
Original (57 KB), tinypng.org (16 KB), pngnq (17 KB):
Using ImageMagick, the best quantization to 256 colors I can get uses the LAB colorspace and dithering by Floyd-Steinberg:
convert input.png -quantize LAB -dither FloydSteinberg -colors 256 output.png
This produces a 16 KB png, but it contains much more visual artifacts: