2/24/2023 0 Comments Imagemagick convert to grayscale![]() This switch is particularly handy for fixing a monochrome picture that was mistakenly encoded as a color JPEG. The luminance channel is preserved exactly, so this is a better method of reducing to grayscale than decompression, This option discards the chrominance channels if the input image is YCbCr (ie, a standard color JPEG), resulting in a grayscale JPEG file. However, while the image data is losslessly transformed, metadata can be removed. Which would not be true if you used djpeg followed by cjpeg to accomplish the same conversion.īut by the same token, jpegtran cannot perform lossy operations such as changing the image quality. Therefore, its transformations are lossless: there is no image degradation at all, Jpegtran works by rearranging the compressed data (DCT coefficients), without ever fully decoding the image. Images with roughly the same mean and standard deviation are probably visually identical.Jpegtran - lossless transformation of JPEG files for %%T in (colour_distance_Lab) do (įrom a single colour image, we have created 42 monochrome images. We can find the distance in any desired colorspace. ^( clone -fill khaki -colorize 100 -negate ^) ^ ^( clone -fill %%H -colorize 100 -negate ^) ^ This simulation is closer, but still inaccurate. We use the negative of the color, and negate the result. We can adapt the previous method to more closely simulate a colour filter over a lens. Most colours in the source photo are darker than this, and the darkest colours are the most distant, so the result resembles a photographic negative with tones reversed. In the samples below, the given colour is "khaki", which is quite light. When the specified colour is black, the effect is identical to "-intensity RMS -colorspace gray". White can be achieved only if the specified colour was in a corner of the colour cube. The lightest tone depends on the distance from the specified colour to the furthest corner of the colour cube, so it is at least 50%. The most distant colours become the lightest. We can find the distance from any given colour. for %%T in (poly) do (īy using floating-point (HDRI) IM and "-auto-level" we prevent clipping. ![]() It is so strong that the pink toes are burnt out. With weights of 3,-1,-1 we implement a very strong red filter. In each pair of parameters, the second is the exponent, which we will set to one. We can use "-poly" to apply any weights we wish to the channels. This artificial image returns the same mean and standard deviation for all channels. The green filter shown here lightens grass. For example, a red filter darkens blue skies, emphasising clouds. The effect is similar to placing a colour filter over the lens of a camera with black and white film. We can use just a single channel of R, G or B. "-colorspace gray" can be used with an intensity setting. ![]() Two colorspaces are specifically for monochrome. IN (YCC,YDbDr,YCbCr,YIQ,YPbPr,YUV,LCH,LCHab,LCHuv,Lab) ^ Next, we convert to one of the colorspaces that record monochrome in the first channel. IN (Rec601Luminance,Rec709Luminance,Rec601Luma,Rec709Luma,Lightness,Average,MS,RMS,Brightness) ^ for %%T in (modulate) do (įor %%H in (HCL,HCLp,HSL,HSI,HSB,HSV) do ( By default this works in HSL colorspace, but we can change this. One method uses "-modulate 100,0,100" to zero the saturation. ![]() Anticipating the numerical result below, the mean value is within the range of greyscale versions but the standard deviation is much higher. The result is black and white only, with no greys. The outer loop is merely a way of creating setting a "Method" for the format string, without having to re-write the format operation every time. The right box show the image generated by the code in the middle box. The middle box contains code that generates a single image. The images are not shown here but are used for regression testing. The left box contains code that generates one or more images and the mean, standard deviation, colorspace and gamma of each. Source image: if not exist toes.png xcopy /y %PICTLIB 130713\toes.png This is a fairly "raw" photo, without saturation increase or sharpening for the web. Set MM_INFO=-precision 4 -format "%%T, %%H, %%, %%, %%, %%\n" -write info:Įcho Method,Parameter,Mean,StdDev,colorspace,gamma>mmList.csvĪ hald clut is not an interesting image, so I'll use a small extract from a photograph. ![]() We will write some results to a text file, with limited precision to aid the elimination of duplicates. Start by creating a source image to show the methods. However, it provides a smaller number of simple methods. ImageMagick has an infinite number of ways of converting a colour image to monochrome. Snibgo's ImageMagick pages Making an image grayscale (monochrome) ![]()
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