PHOTOGRAPHY MADE EASY
Light and Dark
Photographic lighting is the illumination of scenes to be photographed. A photograph simply records patterns of light, color, and shade; lighting is all-important in controlling
the image.
the image.
1
Perceptual Cause and Effect
Lighting creates the 2D pattern of contrast the brain interprets to recognize 3D objects in photographs. In an in-person viewing experience, the brain relies on stereoscopic vision, parallax, shifting focal in addition to the clues created by the highlight and shadow patterns the light on the object creates. When viewing a photo, the brain tries to match the patterns of contrast and color it has seen to those other sensory memories.
«The baseline for what seems "normal" in lighting is the direction and character of natural and artificial sources and the context provided by other clues»
Steve Jobs
Apple CEO
log2(TPM) is simply the log2 of the Transcript Count Per Million.
TPM stands for transcript per million, and the sum of all TPM values is the same in all samples, such that a TPM value represents a relative expression level that, in principle, should be comparable between samples.
TPM is very similar to RPKM and FPKM. The only difference is the order of operations. Here’s how you calculate TPM:
When you use TPM, the sum of all TPMs in each sample are the same. This makes it easier to compare the proportion of reads that mapped to a gene in each sample. In contrast, with RPKM and FPKM, the sum of the normalized reads in each sample may be different, and this makes it harder to compare samples directly.
TPM stands for transcript per million, and the sum of all TPM values is the same in all samples, such that a TPM value represents a relative expression level that, in principle, should be comparable between samples.
TPM is very similar to RPKM and FPKM. The only difference is the order of operations. Here’s how you calculate TPM:
- Divide the read counts by the length of each gene in kilobases. This gives you reads per kilobase (RPK).
- Count up all the RPK values in a sample and divide this number by 1,000,000. This is your “per million” scaling factor.
- Divide the RPK values by the “per million” scaling factor. This gives you TPM.
When you use TPM, the sum of all TPMs in each sample are the same. This makes it easier to compare the proportion of reads that mapped to a gene in each sample. In contrast, with RPKM and FPKM, the sum of the normalized reads in each sample may be different, and this makes it harder to compare samples directly.
Reads Per Kilobase Million.
These three metrics attempt to normalize for sequencing depth and gene length. Here’s how you do it for RPKM:
These three metrics attempt to normalize for sequencing depth and gene length. Here’s how you do it for RPKM:
- Count up the total reads in a sample and divide that number by 1,000,000 – this is our “per million” scaling factor.
- Divide the read counts by the “per million” scaling factor. This normalizes for sequencing depth, giving you reads per million (RPM)
- Divide the RPM values by the length of the gene, in kilobases. This gives you RPKM.
Fragments Per Kilobase Million. FPKM was made for paired-end RNA-seq.
https://www.ebi.ac.uk/gxa/experiments/E-MTAB-4801/Results?specific=true&geneQuery=%255B%257B%2522value%2522%253A%2522TP53BP1%2522%252C%2522category%2522%253A%2522symbol%2522%257D%252C%257B%2522value%2522%253A%2522NUDT16L1%2522%252C%2522category%2522%253A%2522symbol%2522%257D%252C%257B%2522value%2522%253A%2522IAPP%2522%252C%2522category%2522%253A%2522symbol%2522%257D%252C%257B%2522value%2522%253A%2522p300%2522%252C%2522category%2522%253A%2522synonym%2522%257D%252C%257B%2522value%2522%253A%2522TP53%2522%252C%2522category%2522%253A%2522symbol%2522%257D%252C%257B%2522value%2522%253A%2522MDM2%2522%252C%2522category%2522%253A%2522symbol%2522%257D%252C%257B%2522value%2522%253A%2522MDMX%2522%252C%2522category%2522%253A%2522synonym%2522%257D%255D&filterFactors=%257B%257D&cutoff=%257B%2522value%2522%253A0.5%257D&unit=%2522TPM%2522
https://www.ebi.ac.uk/gxa/experiments/E-MTAB-2770/Results?specific=true&geneQuery=%255B%257B%2522value%2522%253A%2522ENSG00000269622%2522%257D%252C%257B%2522value%2522%253A%2522TP53%2522%252C%2522category%2522%253A%2522symbol%2522%257D%252C%257B%2522value%2522%253A%2522MDM2%2522%252C%2522category%2522%253A%2522symbol%2522%257D%252C%257B%2522value%2522%253A%2522MDMX%2522%252C%2522category%2522%253A%2522synonym%2522%257D%252C%257B%2522value%2522%253A%2522p300%2522%252C%2522category%2522%253A%2522synonym%2522%257D%252C%257B%2522value%2522%253A%2522IAPP%2522%252C%2522category%2522%253A%2522symbol%2522%257D%252C%257B%2522value%2522%253A%2522NUDT16L1%2522%252C%2522category%2522%253A%2522symbol%2522%257D%252C%257B%2522value%2522%253A%252253BP1%2522%252C%2522category%2522%253A%2522synonym%2522%257D%255D&filterFactors=%257B%2522CELL_LINE%2522%253A%255B%2522AU565%2522%252C%2522CAL-120%2522%252C%2522CAL-148%2522%252C%2522CAL-85-1%2522%252C%2522CAMA-1%2522%252C%2522HCC1428%2522%252C%2522Hs%2520274.T%2522%252C%2522MDA-MB-231%2522%252C%2522MDA-MB-361%2522%252C%2522MDA-MB-415%2522%252C%2522MDA-MB-453%2522%252C%2522MDA-MB-468%2522%252C%2522SK-BR-3%2522%255D%257D&cutoff=%257B%2522value%2522%253A0.5%257D&unit=%2522TPM%2522
2
The Natural Light Baseline
To differentiate that role from that of "key" modeling when a modeling source moves behind the object, it is typically called a "rim" or "accent" light. In portrait lighting, it is also called a "hair" light because it is used to create the appearance of physical separation between the subject's head and background.
When a photographer puts the sun behind an object, its role in the lighting strategy changes from modeling the front of the object to one of defining its outline and creating the impression of physical separation and 3D space a frontally illuminated scene lacks.
Steve Jobs
Apple CEO
1818 Magazine by Stephanie Toole
To differentiate that role from that of "key" modeling when a modeling source moves behind the object, it is typically called a "rim" or "accent" light. In portrait lighting, it also called a "hair" light because it is used to create the appearance of physical separation between the subject's head and background.
3
Creating Natural Looking Artificial Lighting
A typical studio lighting configuration will consist of a fill source to control shadow tone, a single frontal key light to create the highlight modeling clues on the front of the object facing the camera over the shadows the fill illuminates, one or more rim/accent lights to create separation between foreground and background, and one or more background lights to control the tone of the background and separation between it and the foreground.
There are two significant differences between natural lighting and artificial sources. One is the character of the fill and the other is a more rapid fall-off in intensity. In nature, skylight fill is omni-directional and usually brighter from above. That "wrap around" characteristic is difficult to duplicate with a directional artificial source.
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